Robsten are finally doing it! At least, for you to all enjoy on screen.

As we've already dished, there is going to be more sex (finally!) in the last Twilight flicks. Even though it will have a PG-13 rating, the studio is leaving a lot up to director Bill Condon to decide how to shoot the racy stuff.

But if Bill sticks to the script, we're told by sources on set that one Twilight star is going to be stripping down...way down.

"The script actually has Kristen practically naked in it, a lot," ‘fesses a source who took a peek (at the script, not K.Stew, sickos).

Obviously you won't see Stewart's bod actually end up on the big screen, (remember as our source emphasizes "rating is key"), but Condon is the type of director who likes to keep it real, shoot it real, then edit it in a way that is über-hot when it hits theaters.

Hey, Kristen has done it for roles before, and we all know she's super comfortable around Rob. Only complaint? Let's make it equal and have R.Pattz equally bare. Yeah?

Oh, and some not-so-hot news from down south: Apparently the wedding dress Bella wears isn't as hot as the sex scenes.

"It's hideous," dishes our insider. "And it's not the designer's fault. Let's just say someone who has final say on the matter has decided upon a terribly conservative and ugly gown."